Echocardiographic studies of ventricular septal motion were performed in patients with right ventricular volume overload, left ventricular volume overload, right ventricular pressure overload, left ventricular pressure overload, and in normal subjects, to define the determinants of septal motion. In each group, the direction and magnitude of septal motion during systole was predicted by the intracardiac position of the septum at end-diastole. Thus, paradoxic septal motion, while usually seen in conditions causing right ventricular volume overload, is actually only dependent upon the geometric position of the septum within the heart, and is not etiologically specific.